The Shuttle Orbiter, the only operational Reusable Launch Vehicle (RLV), is protected during ascent and reentry by lightweight, low thermal conductivity rigid and flexible thermal protection systems (TPS). The Shuttle Orbiter currently uses various thermal protection systems to mitigate aerothermal heating encountered during ascent/reentry. At high temperatures (up to 1500° F.) quilted ceramic blankets are used for thermal protection. At extreme temperatures, (up to 3000° F.) rigid ceramic materials such as porous silica tile and carbon-carbon materials provide protection against thermal burn-through. For low temperature uses (up to 750° F.) felt batting systems such as the Flexible Reusable Surface Insulation (FRSI) system are used. The FRSI system consists of Nomex™ batting needled into a large felt-type pad/sheet and coated with a protective silicone topcoat. The coated pad is used on the Shuttle Orbiter in areas that have limited thermal requirements, i.e., areas that have relatively low aerothermal heating (up to 750° F.). The advantage of the FRSI system is that it can be easily installed in large part sizes onto the vehicle because of its flexible needled-felt construction.
The robust nature, simple design, and conformability of the current FRSI system make it well suited for extensive use since it can easily withstand acoustic loading and provide a smooth continuous aerodynamic surface. However, the inherent material properties of the Nomex™ batting and silicone coating that compose FRSI limit the temperature capability of this product to areas that remain below 750° F. such as the top surface of the fuselage and the upper surfaces of the wings. This limitation in thermal stability is unfortunate since its simplicity in design, low cost, low maintenance, and ease in installation make FRSI an excellent candidate for more extensive use if the upper temperature limit were raised.
While other non-FRSI thermal protection systems are used at present to manage the thermal requirements over the higher temperature areas of the Orbiter vehicle during ascent and reentry, these other systems are more expensive relative to FRSI in terms of installation, maintenance, and replacement. Furthermore, the simplicity in design of FRSI allows it to be easily cut to accommodate any size or shape, whereas other thermal protection systems must be custom fabricated, which results in higher manufacturing costs. What is needed is an insulating material exhibiting the ease of manufacture and ease of installation associated with FRSI while exhibiting improved thermal insulating characteristics.